Copolymers and terpolymers, when isolated from reaction solution are a mixture of compounds of varying composition and molecular weight. Typically they contain small quantities of starting material and by-products which are undesirable in the final polymer. The polymer mixture is precipitated from the solvent or solvent mixture by adding the mixture to a second solvent, as for example water, hexane, heptane, octane, petroleum ether, or a mixture thereof. The polymer is then dried under a nitrogen atmosphere. The subject of this invention pertains to a method of purifying the polymer.
Davidson, in U.S. Pat. No. 5,945,251, discloses a method of purifying polyhydroxystyrene polymers by adding an amine, a hydrophilic solvent, a hydrophobic solvent, and water to the polymer; separating the aqueous phase; then removing the hydrophilic solvent and the hydrophobic solvent to form the purified polymer.
Zempini, et al. in U.S. Pat. Nos. 5,789,522 and 5,939.511, extracts impurities from a phenolic resin by dissolving the resin in a photoresist solvent and extracting the water-soluble impurities therefrom.
The present invention provides a novel process for improving the glass transition temperatures and reducing the polydispersity values of polymer intermediates that have been polymerized by precipitation from methanol. The polymers that are susceptible to treatment with the method of this invention are polymers of 4-acyloxystyrene. The 4-acyloxystyrene derived polymers are then transesterified to 4-hydroxyphenyl-containing polymers useful in paints, resins, thickening agents, and in photoresist compositions. The present invention process is an improvement over the prior art and is quite efficient. Specifically the invention provides a method of removing unreacted monomers, low molecular weight polymers, and the like from the crude polymer mixture before the transesterification step. Many analytical methods can be utilized to quantify the improvement in the purity of polymers. Average molecular weight, nuclear magnetic resonance, chromatography, and glass transition temperature are all effective in certain instances with certain molecules and characteristic side chains.
As previously described in the prior art, the crude polymer after polymerization is separated from the alcohol by filtration, centrifugation, decantation, or the like. According to the method of this invention, the polymer is subject to fractionalization whereby it is suspended in methanol and the solid is separated from the methanol. This procedure is repeated as long as necessary to remove by-products and low molecular weight materials that are more soluble in the methanol than the desired polymer. In this manner, the undesirable monomeric impurities and oligomers are soluble in the solvent (such as methanol) depending upon temperature and thus are removed during each fractionation step.
This invention provides a process for the improvement in the composition of polymers derived from the monomer I, 
wherein R is either xe2x80x94C(O)R5 or xe2x80x94R5; as a homopolymer and/or typically with one or more of the following monomers: an acrylate monomer having the formula II, 
and/or with one or more ethylenically unsaturated copolymerizable monomers (EUCM) selected from the group consisting of styrene, 4-methylstyrene, styrene alkoxide wherein the alkyl portion is C1-C5 straight or branch chain, tert.-butylstyrene, cyclohexyl acrylate, tert.-butyl acrylate, tert.-butyl methacrylate, maleic anhydride, dialkyl maleate, dialkyl fumarate and vinyl chloride. wherein:
i) R1 and R2 are the same or different and independently selected from the group consisting of:
hydrogen;
fluorine, chlorine or bromine;
alkyl or fluoroalkyl group having the formula CnHxFy where n is an integer from 1 to 4, x and y are integers from 0 to 2n+1, and the sum of x and y is 2n+1; and phenyl or tolyl;
ii) R3 is selected from the group consisting of:
hydrogen; and
methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl or tert.-butyl;
iii) R4 is methyl, ethyl, n-propyl, iso-propyl or tert.-butyl; and
iv) R5 is C1-C4 alkyl, typically manufactured by subjecting a monomer of formula I, 
or a monomer of the formula I and/or monomer II, and/or one or more of said copolymerizable monomers (EUCM) to suitable polymerization conditions in an alcoholic solvent and in the presence of a free radical initiator at suitable temperature for a sufficient period of time to produce a crude polymer of corresponding composition. After purification by the method of this invention, the purified polymer is transesterified to a polymer containing the monomer of formula III: 
by (1) subjecting said polymer to transesterification conditions in said alcoholic solvent in the presence of catalytic amounts of a base catalyst at suitable temperature such that the transesterified by-product ester formed is continuously removed from the reaction mixture to form the homopolymer of I or the copolymer of I, and/or II, and/or said copolymerizable monomer, (EUCM) or
(2) subjecting the polymer to acidic hydrolysis with a strong acid. The polymer is then optionally passed through an ion-exchange bed to remove said base or acid catalyst;
The polymerization, purification, and/or transesterification steps are carried out on an anhydrous basis (i.e.  less than about 5,000 ppm water). The alcoholic solvent for the polymerization is an alcohol having 1 to 4 carbon atoms and is selected from the group consisting of methanol, ethanol, propanol, isopropanol, t-butanol, and combinations thereof. The amount of solvent used is not critical and can be any amount which accomplishes the desired end result.
The free radical initiator for the polymerization may be any initiator that achieves the desired end result. The initiator may be selected from the group consisting of 2,2xe2x80x2-azobis(2,4-dimethylpentanenitrile), 2,2xe2x80x2-azobis(2-methylpropanenitrile), 2,2xe2x80x2-azobis(2-methylbutanenitrile), 1,1xe2x80x2-azobis(cyclohexanecarbonitrile), t-butyl peroxy-2-ethylhexanoate, t-butyl peroxypivalate, t-amyl peroxypivalate, diisononanoyl peroxide, decanoyl peroxide, succinic acid peroxide, di(n-propyl) peroxydicarbonate, di(sec-butyl) peroxydicarbonate, di(2-ethylhexyl) peroxydicarbonate, t-butylperoxyneodecanoate, 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane, t-amylperoxyneodecanoate, dimethyl 2,2xe2x80x2-azobisisobutyrate, and combinations thereof.
The initiator is typically selected from the group consisting of 2,2xe2x80x2-azobis(2,4-dimethylpentanenitrile), 2,2xe2x80x2-azobis(2-methylpropanenitrile), 2,2xe2x80x2-azobis(2-methylbutanenitrile), 1,1xe2x80x2-azobis(cyclohexanecarbonitrile), t-butyl peroxy-2-ethylhexanoate, t-butyl peroxypivalate, t-amyl peroxypivalate, and combinations thereof.
The polymerization conditions are not critical and can be any temperature and pressure that will produce the desired end result. In general, the temperatures are from about 30xc2x0 C. to about 100xc2x0 C., preferably from about 40xc2x0 C. to about 100xc2x0 C., and most preferably from about 45xc2x0 C. to about 90xc2x0 C. The pressure may be atmospheric, sub-atmospheric or super-atmospheric. The polymerization time is not critical, but generally will take place over a period of at least one minute in order to produce a polymer of corresponding composition.
After the polymerization step and prior to the transesterification step, the crude polymer is subjected to a purification procedure wherein the same type carboxylic alcoholic solvent (first solvent) is used to purify the crude polymer via a multi-step fractionation process. Additional first solvent is added to the crude polymer mixture, and the resultant slurry is stirred vigorously and/or heated to boiling (about 66xc2x0 C.) for several minutes, and then chilled to as low as 25xc2x0 C. and allowed to stand. This permits the slurry to produce a phase separation, and then the liquid is removed by centrifugation, filtration, decantation or by similar means. The process is repeated at least one more time until no further purification is identified, as for example, until a small sample of the decanted solvent, upon evaporation to dryness shows substantially no residue. This fractionation process is generally carried out 2 to 10 times, i.e. heating, cooling, separating, and the solvent replacement.
One of the important measures of the degree of impurity of the crude polymer produced from the polymerization of the monomers is the polydispersity value. In general, it is desirable to have a low value, for example, less than about 3; the lower value is indicative that the polymerization reaction was more uniform in chain length. The uniqueness of this purification step is that the desired polymer formed is to some degree not soluble in the solvent and that the undesired, low molecular weight average polymers and undesired monomers are soluble in the solvent. Thus the novel purification/fractionalization step, provides the removal of these undesirable materials. In general the polydispersity of the crude polymer is measured before, during and after this purification/fractionalization step, with the objective of reducing this value by at least about 10% of what the value of the original crude polymer was before the purification treatment. Preferably it is desirable to yield a product whose polydispersity is below about 2.0. It is to be understood that polydispersity means the ratio of weight average molecular weight (Mw) over the number average molecular weight (Mn) as determined by Gel Permeation Chromatography (GPC).
In the transesterification step, the purified polymer from the polymerization step is subjected to said transesterification conditions in an alcoholic solvent in the presence of catalytic amounts of a base catalyst. The base catalyst is such that it will not substantially react with said alkyl acrylate monomer II, or with said co-polymerizable monomers (EUCM). The base catalyst is either an alkalic metal hydroxide or an alkalic metal alkoxide. The base catalyst is selected from the group consisting of lithium hydroxide, lithium methoxide, lithium ethoxide, lithium isopropoxide, sodium hydroxide, sodium methoxide, sodium ethoxide, sodium isopropoxide, potassium hydroxide, potassium methoxide, potassium ethoxide, potassium isopropoxide, cesium hydroxide, cesium methoxide, cesium ethoxide, cesium isopropoxide, and combinations thereof.
If a hydrolysis is utilized to effect removal of the phenol blocking group, the acid should be a member of the strong acids, as for example hydrochloric acid, hydrobromic acid, sulfuric acid, or the like.
Thus and according to the method of this invention, after polymerization of the acyloxy-derived polymer, and prior to the transesterification the crude polymer is subjected to this novel fractionation process which provides a substantially purified polymer which then can be further treated.
This invention is further illustrated by the following examples that are provided for illustration purposes and in no way limits the scope of the present invention.